Multimedia service continuity has been introduced in 3rd generation partnership project (3GPP) release 8. The multimedia service continuity implies that, when an access network (AN) changes or a user equipment (UE) used by a user changes, an ongoing multimedia session is continued by using the changed AN or the changed UE. The multimedia service continuity is provided to use a seamless multimedia service when the UE under the multimedia service attempts access through another AN or when the user transfers media of the ongoing multimedia session to another UE.
Several scenarios have been introduced in association with the multimedia service continuity. Examples of the scenarios include ‘PS-PS session continuity’ which denotes multimedia session continuity when a multimedia session is transferred between different packet switched (PS) ANs, ‘PS-PS session continuity in conjugation with PS-CS continuity’ which denotes multimedia session continuity when media sessions on a PS domain and a circuit switched (CS) domain are transferred to one PS AN, or the other way around, and ‘UE transfer’ which denotes session continuity when a media component is transferred between different UEs controlled by the same user.
The scenarios in association with the multimedia service continuity may be a procedure in which all or some of the ongoing multimedia components are transferred to another AN and/or another UE. According to the 3GPP release 8, ‘multimedia session transfer’ or simply ‘session transfer’ is defined as transfer at an IP multimedia subsystem (IMS) level in session signaling paths and media paths of an ongoing session while maintaining session continuity.
The multimedia session transfer can be realized by AN transfer and/or UE transfer. The AN transfer implies a change of an AN from a UE to an IMS core, that is, a change of a network core of a radio access network (RAN) (e.g., a base station (BS)) and/or an Internet protocol-connectivity access network (IP-CAN). On the other hand, the UE transfer implies session transfer between different UEs controlled by the same user. For example, this is a case where all media components or some media components of an ongoing multimedia session are transferred to any one of the UEs to another UE.
To achieve the multimedia service continuity, there is a method employing a session anchoring mechanism using the IMS core. More specifically, a specific application server for providing the multimedia service continuity (e.g., a multimedia session continuity application server (MMSC AS)) may be installed in the IMS core so that all ongoing control signals and data signals are transmitted through the MMSC AS. Further, when there is a session transfer request, all or some media components of the ongoing multimedia session are allowed to pass through another AN with respect to the MMSC AC and/or are allowed to communicate with another UE.                Advantageously, the session anchoring mechanism using the MMSC AS can support the multimedia service continuity through session transfer without having to significantly depend on an AN type, a UE type, a media component characteristic, etc. Disadvantageously, however, the mechanism is not much effective since it is premised that control signals and data signals for session transfer are delivered up to the IMS core, i.e., the MMSC AS. An additional procedure (e.g., IMS registration) may be required.        